Conventional semiconductor packages for optical communication include metal packages and CAN packages. A metal package is a combination of a multilayer ceramic substrate and a metallic box. A CAN package has a metal plate, a metallic rod passed through an open hole in the metal plate and hermetically sealed and insulated with glass, and a welded cap with a window.
The metal package has an excellent high-frequency characteristic because of use of the multilayer ceramic substrate. The metal package, however, has a complicated structure and a large number of parts and is high in cost. Also, because of its box form, parts can be mounted only from the opening side (upper side) before the package is closed.
In the case of the CAN package, parts can be mounted from all directions onto the upper surface of the metal plate, and the metal plate and the cap can be joined to each other in an instant by electric welding. The CAN package therefore has high producibility. However, since the lead for supplying a signal is fixed by glass sealing on the metal plate, it is difficult to achieve impedance matching thereat and the CAN package is inferior in high-frequency characteristic.
A semiconductor package has been proposed which has an optical semiconductor element mounted in a recess in an upper surface of a multilayer ceramic substrate and covered with a metallic cap with a window (see, for example, Patent Literature 1).